(1). Field of the Invention
The present invention relates to an image forming apparatus utilizing an electrophotographic system, for example, and specifically, to an image forming apparatus that performs image formation while transporting recording materials substantially in a vertical direction.
(2). Description of the Related Art
In an image forming apparatus such as a copier and printer utilizing an electrophotographic system, for example, a photoconductor of a drum shape (photoconductor drum) is uniformly charged, the photoconductor drum is exposed to light controlled based on image information, and an electrostatic latent image is formed on the photoconductor drum. Then, the electrostatic latent image is turned into a visible image (toner image) with toner, and the toner image is transferred from the photoconductor drum to a recording material in a transfer part, and the toner image is fixed onto the recording material by a fixing device.
As the fixing device used for such an image forming apparatus, generally, a device including a fixing roll formed by laminating a heat-resistant elastic material layer and a release layer on a cylindrical core provided with a heating source therein and a pressure roll formed by laminating a heat-resistant elastic material layer and a release layer composed of a heat-resistant resin coating or heat-resistant rubber coating on a core in pressure contact with each other is used. In this configuration, a recording material carrying an unfixed toner image is passed through between the rotating fixing roll and pressure roll for heating and pressurizing the unfixed toner image, and thereby, the toner image is fixed onto the recording material.
For such an image forming apparatus, an arrangement in which the above fixing device is disposed above the photoconductor drum in a vertical direction, a transporting path for upwardly transporting substantially in the vertical direction a recording material fed from a paper tray disposed below the photoconductor drum in the vertical direction is formed, and thereby, a toner image on the photoconductor drum is transferred onto the recording material by a transfer member disposed along the transporting path and the recording material is transported to the fixing device has been known.
The image forming apparatus having such an arrangement requires only a very short transporting path for transporting the recording material, and further, a large part of the transporting path can be exposed only by opening one side surface of the image forming apparatus. Accordingly, output time from feeding paper to ejecting paper can be shortened and the transportation of the recording material can be improved, and further, removal of the recording material when a paper jam occurs is easy. Furthermore, the installation area of the image forming apparatus can be easily designed smaller.
However, in the image forming apparatus in which the recording material is transported upwardly substantially in the vertical direction (vertically transported), since the fixing device is provided in a position where the recording material is transported from below upward against gravitational force, when the recording material after fixing in the fixing device is transported, the direction of gravitational force acting on the recording material ejected from the fixing device is substantially on the same line as the transporting direction of the recording material but opposite in direction. Accordingly, unlike a conventional image forming apparatus in which a recording material is transported in a horizontal direction, in the vertically transporting image forming apparatus, it is configurationally difficult to stably support the recording material during transporting utilizing gravitational force, and the behavior of the recording material is likely to be unstable. That is, since it is difficult to stably support the recording material in the horizontal direction with respect to the recording material transported upwardly substantially in the vertical direction by the rotating fixing roll and pressure roll in pressure contact with each other, the recording material becomes unstable in the horizontal direction. Accordingly, the traveling directions of the recording materials are not determined in a certain direction, and wavy wrinkles (so-called “paper cockles”) in the traveling direction become easier to occur in the recording materials. In addition, the recording material becomes easier to come into contact with members around the transporting path, and, depending on the contact angle at that time, bending and folding of both lead edges of the recording material (so-called “dog-ears”) may possibly occur.